Method for operating an internal combustion engine having two inlet valves

ABSTRACT

The invention relates to a method for controlling an internal combustion engine, which has a first inlet valve (P) and a second inlet valve (S) per cylinder, which can be operated independently of one another between maximum operation (P 1 , S 1 ) and minimum operation. The change of the inlet valves takes place preferably by engine oil pressure, in a basic state (P 1 +S 2 ) the first inlet valve (P) is in maximum operation (P 1 ) and the second inlet valve (S) is in minimum operation (S 2 ). From the basic state, the valve control device switches the first inlet valve (P) into a minimum operation (P 3 ) at low engine rotational speeds/engine torques and sufficient engine oil pressure and switches the second inlet valve (S) into maximum operation (S 1 ) at high engine rotational speeds/engine torques.

FIELD OF THE INVENTION

[0001] The invention is a method for operating an internal combustionengine having a first and a second inlet valve in one cylinder, whichare capable of being changed independently between maximum operation andminimum operation. The invention relates, furthermore, to an internalcombustion engine for carrying out a method of this type.

BACKGROUND OF THE INVENTION

[0002] Motor vehicle engines with spark ignition, which, in practice,use almost exclusively gasoline as fuel, are operated predominantly witha stoichiometric air/fuel mixture, which allows highly efficienttreatment of the exhaust gas emissions. Torque control is provided bythrottling. In part load operation of such an engine, however, fuelconsumption increases due to throttling and to stoichiometric operation.These losses can be reduced by homogeneous or stratified lean operation,although this has the disadvantage that the NOx emissions of the enginecannot be treated at high efficiency by a conventional three-waycatalytic converter. Three-way catalysts with NOx trapping capabilityare considerably more costly than conventional three-way catalyticconverters are used to remove nitrogen oxides for lean burning systems.Furthermore, when stratified direct injection is employed, the systemsfor the provision of air, fuel, exhaust gas recirculation, and ignitionare also all considerably more complex and costly than in a conventionalengine. Even pressure charging, for improving fuel consumption instoichiometric operation, is more costly due to the turbocharger withintermediate cooler.

SUMMARY OF THE INVENTION

[0003] A more cost-effective approach to improving engine efficiency isby variable valve control in which the opening durations, closing times,and/or valve stroke of the inlet valves and/or the exhaust valves isadjusted. One alternative to provide variable valve control is for thevalve control device to have two or three valve opening profiles(referred to briefly below as “valve profiles”), which differ in termsof duration and/or valve stroke.

[0004] Furthermore, in internal combustion engines having two or moreinlet valves per cylinder, the inlet valves of a cylinder may beequipped in each case with variable valve controls, which areindependent of one another, thus allowing a multiplicity of controlpossibilities for engine operation.

[0005] Against this background, the object of the present invention wasto provide means for efficient operation of an internal combustionengine having a plurality of inlet valves per cylinder, which can bechanged independently of one another between minimum operation andmaximum operation.

[0006] A method operate an internal combustion engine which has at leastone cylinder with at least one first and one second inlet valve isdisclosed. Preferably, the first inlet valve is arranged in a primaryinlet duct, via which the main quantity of fresh air is supplied, andthe second inlet valve is arranged in a secondary inlet duct, via whicha smaller quantity of air for swirling is supplied. The inlet valves arecapable of being changed independently from each other between:

[0007] (a) maximum operation, which is defined by a larger valve strokeand/or a longer opening duration, and

[0008] (b) minimum operation, which is defined by a smaller valve strokeand/or a short opening duration.

[0009] The shorter valve opening durations in minimum operationpreferably are such that they lie completely within the valve openingdurations in maximum operation. Moreover, the valve opening duration inminimum operation is preferably shorter than the intake stroke of theinternal combustion engine. The method is defined in that, in a basicstate, the first inlet valve is used in maximum operation and the secondinlet valve in minimum operation.

[0010] In the method described, by the relatively simple changeover ofvalve operation between two types of operation (minimum operation,maximum operation), a broad spectrum of control possibilities can becovered since two inlet valves of a cylinder can be changedindependently. In theory, by a combination of the various types ofoperation of the two inlet valves, a minimum of four operating modes canbe set for the internal combustion engine. According to the method, anoperating mode, in which the first of the inlet valves is used inmaximum operation and the other inlet valve is used in minimumoperation, serves as a basic state, which is assumed during most of thetime of the “normal” driving operation of a motor vehicle, i.e., themost commonly used rotational speed and torque ranges. The advantage ofa basic state of this kind, with mixed maximum and minimum operation ofthe inlet valves, is that this constitutes an optimum starting pointboth for an increase in power of the internal combustion engine and fora transition to minimum power requirements, for example during idling.Furthermore, owing to the maximum operation of one of the inlet valves,the basic state makes available a certain minimum performance of theinternal combustion engine, which ensures a reliable functioning ofconnected assemblies such as, for example, an alternator, or of pressurepumps, and therefore the controllability of the motor vehicle functions.At the same time, due to the minimum operation of the other inlet valve,an asymmetric air inlet and consequently a high swirling in the cylinderare achieved. This leads to a good mixing of air and fuel and to goodcombustion. The basic state thus has advantageous properties also withregard to fuel utilization and engine efficiency. The basic state ispreferably implemented automatically by the inlet valves in the event ofthe absence of active (that is to say, energy requiring) control of theinlet valves. That is to say, the basic state is a default state whichis assumed automatically in the event of a possible anomaly of valvecontrol owing to the mixing of maximum operation and minimum operation,reliable engine operation is ensured in the basic or default state.

[0011] Alternatively, the changeover of the inlet valve between minimumoperation and maximum operation is brought about by the pressure of theengine oil. In the event of a low engine oil pressure below apredetermined threshold value, the inlet valves are operated in thebasic state. The basic state is therefore assumed automatically wheneverthe available engine oil pressure is insufficient for switching theinlet valves, for example because the engine has been idling for arelatively long time, because there is a high oil temperature or becausethe oil system is disrupted. In the basic state, a spontaneous increasein power of the internal combustion engine is therefore possible fromidling, the increased power subsequently ensuring an increase in theengine oil pressure and thus ensuring the complete switchability of thevalve control.

[0012] In one embodiment, the capacity of the inlet valves to changeindependently of one another is used to operate the engine optimallyaccording to the following. In the case of a low to medium enginerotational speed and a low to medium engine torque, both inlet valvescan be used in minimum operation. When both inlet valves are in minimumoperation, the air quantity supplied and consequently also theassociated fuel consumption are minimum. If, as described above, thechangeover of the inlet valve takes place with the aid of the engine oilpressure, the operating state of minimum operation of both inlet valvesis carried out preferably only in the case of a sufficiently high engineoil pressure or in the case of an engine oil temperature which has notincreased, so that the capability of the inlet valves to change over andconsequently the transition into another operating state remain possibleat any time. In the case of a high engine rotational speed and/or a highengine torque, both inlet valves are used in maximum operation toprovide as much air as possible.

[0013] The transition from one operating mode to another operating modeof the inlet valves preferably takes place in such a way that only oneof the inlet valves changes its type of operation. Thereby, changes inengine behavior associated with the inlet valve mode change are kept assmall as possible, so that they are noticed to the least possible extentby the driver or can be compensated relatively simply by other devicessuch as a change in the throttle setting, spark timing or in fuelinjection. An operating mode change of this kind due to a change in thetype of operation of only one inlet valve is implemented in the chain ofthe above-described operating modes (both inlet valves in minimumoperation; basic state; both inlet valves in maximum operation).

[0014] The valve stroke and/or the valve opening duration of the firstinlet valve in minimum operation are/is preferably shorter than thecorresponding size when the second inlet valve is in minimum operation.In particular, the maximum valve stroke of the first inlet valve inminimum operation may be less than 40%, preferably less than one third,of the maximum valve stroke of the second inlet valve in minimumoperation. Thereby, when both inlet valves are in minimum operation,most air is sucked in through the second inlet valve, thus ensuring highswirling in the cylinder due to the asymmetry.

[0015] The valve stroke of the second inlet valve in the minimumoperation is preferably less than 40%, particularly less than one third,of the valve stroke of the first inlet valve in the maximum operation.During the basic state, therefore, the predominant fraction of the inletair flows through the first inlet valve with a relatively low flowresistance. By contrast, considerably less air flows through the secondinlet valve, although the corresponding quantity advantageously bringsabout swirling in the cylinder.

[0016] The invention relates, furthermore, to an internal combustionengine which contains the following components:

[0017] a) At least one cylinder with at least two inlet valves.

[0018] b) A variable valve control device which can changeover the inletvalves independently of one another between (a) maximum operation with alarger valve stroke and/or a longer opening duration and (b) minimumoperation with a small valve stroke and/or a shorter opening duration.The valve control device may contain, in particular, a camshaft withdifferent inlet cams for minimum operation and maximum operation,between which the changeover can be made.

[0019] c) An engine control which is connected to the valve controldevice and is set up to operate the internal combustion engine accordingto a method of the type explained above. That is to say, in a basicstate, the first inlet valve is used in maximum operation and the secondinlet valve in minimum operation. The internal combustion engine or theengine control may be developed in such a way that it can also implementthe variants of said method.

[0020] According to the preferred development of the internal combustionengine, the valve control device is connected to the engine oil systemof the internal combustion engine and is designed to change over theinlet valves by means of selective action by an engine oil pressure. Theuse of the engine oil pressure for switching purposes has the advantagethat known hydraulic methods can be adopted. Preferably, furthermore,the valve control device is set up to operate the first inlet valve inmaximum operation and the second inlet valve in minimum operation whenthe engine oil pressure lies below a predetermined threshold pressure.This setting thus constitutes a default state which is assumed when, forany reason, the engine oil pressure is not sufficient for changeoveroperation.

[0021] The invention is explained in more detail below by way of examplewith the aid of the Figures of which:

[0022]FIG. 1 is a graph of valve stroke versus crank angle for inlet andexhaust valves ∘ an internal combustion engine showing three operatingstates;

[0023]FIG. 2 is a graph of the full torque curves in an engine stategraph of the torque versus engine rpm for the three operating states ofthe inlet valve, as illustrated in FIG. 1;

[0024]FIG. 3 is a schematic of the first and second inlet valves in theport of an internal combustion engine and graphs of the associated typesof operation according to the invention of the valves; and

[0025]FIG. 4 is a graph of the full torque curve in an engine stategraph of the torque versus engine rpm showing the engine control,according to the present invention, indicating operating mode.

DETAILED DESCRIPTION

[0026]FIG. 1 shows diagrammatically the valve profiles of an exhaustvalve EX and of an inlet valve IN of the valve stroke H (vertical axis)against crankshaft angle (horizontal axis) where TDC is top dead centerand BDC is bottom dead center of piston travel. The inlet valve, whichis of interest in the present case, is operated by means of a valvecontrol device capable of being changed over between three states 1, 2,3, so that three valve profiles of the inlet valve are possible:

[0027] 1: Maximum operation under full torque, the valve openingduration being longer than the intake stroke;

[0028] 2: Intermediate operation for medium torques, the valve openingduration being shorter than the intake stroke;

[0029] 3: Minimum operation for engine idling with a very short openingduration and with a small maximum valve stroke.

[0030] With reduced valve opening duration in intermediate operation 2,the pumping loss normally associated with throttling of the engine canbe reduced. Since the inlet valve is open for a shorter duration and/orstroke, the manifold pressure is raised. Consequently, the pressure dropacross the throttle is less and the engine performs less pumping work toinduct the desired amount of air into the cylinder.

[0031]FIG. 2 shows, in an engine state graph of torque, T, of theinternal combustion engine versus engine rotational speed, n, the threefull torque curves 1, 2 and 3 for wide open throttle operation for valveoperation modes 1, 2 and 3, according to FIG. 1. Reduced valve strokeand valve opening duration reduces the achievable torque at all enginespeeds. The minimum operation 3 of the inlet valve can be utilized, forexample, only in a small region of area around the idling rotationalspeed n0. The intermediate operation 2 of the inlet valve affords thegreatest advantages in the range of medium engine rotational speeds andof low torques. By contrast, maximum operation 1 opens up the entireoperating field of the internal combustion engine, but has no advantageswith regard to fuel consumption.

[0032] At idle, therefore, the minimum operation 3 of the inlet valve ispreferable, and, in the event of an actuation of the accelerator pedalby the driver as command for spontaneous acceleration, a rapidchangeover into intermediate operation 2 or, if a particularly sharpacceleration were required, even into maximum operation 3. However, inhydraulically switched valve control devices used conventionally, such avalve control leads to problems, since, during idling, engine oilpressure is typically insufficient for changing over the actuators. Thisis exacerbated by increased oil temperatures such that a sufficientengine oil pressure for changing over the actuators becomes availableonly at medium engine rotational speeds.

[0033] This could be overcome, in principle, by an oil pump having ahigher performance than otherwise be used. However, this would largelynullify the advantages achieved by variable valve control. Thus, a valvecontrol device which can change over between (at least) two types ofoperation of the inlet valves (minimum operation, maximum operation) isdesired.

[0034] In this regard, FIG. 3 shows the valve device on which thesolution according to the invention is based. The upper part of FIG. 3illustrates a part of a cylinder head of an internal combustion enginewith a first inlet valve P and with a second inlet valve S. Fresh air issupplied to the inlet valves via an intake manifold 10, the intakemanifold 10 being divided into a primary inlet duct 11 to the firstinlet valve P and a secondary inlet duct 12 to the second inlet valve S.The configuration of the ducts and the inlet valves P, S is preferablysuch that the air supplied through the second inlet valve S generatesswirl in the cylinder to create turbulence to enhance the ensuingcombustion of the air and fuel.

[0035] The two inlet valves are capable of being changed independentlyof one another between various types of operation with the aid of theengine oil pressure. The lower part of FIG. 3 illustrates these types ofoperation of the two inlet valves P, S as valve profiles in the graph ofthe valve stroke H against the crankshaft angle. Accordingly, the twoinlet valves P, S have a maximum operation P1 and S1 with a largemaximum valve stroke and with a long valve opening duration. Inparticular, the valve opening duration is preferably longer than theintake stroke of the internal combustion engine. The valve profiles P1and S1 of the two inlet valves are otherwise similar to one another.

[0036] Furthermore, the two inlet valves may also be operated in eachcase in minimum operation P3 and S2. In this case, they have very muchsmaller maximum valve strokes and/or shorter valve opening durationsthan in maximum operation P1 or S1. In particular, the valve openingduration is shorter than the intake stroke of the internal combustionengine.

[0037] Moreover, FIG. 3 indicates that

[0038] in minimum operation, P3, of the first inlet valve, P, themaximum valve stroke is only about one third of the maximum valve strokeof the second inlet valve S in minimum operation S2 of the latter; and

[0039] the maximum valve stroke of the second inlet valve S in minimumoperation S2 of the latter is only about one third of the maximum valvestroke of the first inlet valve P in maximum operation, P1, of thelatter.

[0040]FIG. 4 shows an engine state graph (corresponding to FIG. 2) forthe internal combustion engine or valve control discussed above withreference to FIG. 3. The possibility of being able to change over twoinlet valves, P, S, of a multi-valve internal combustion engineindependently between various cam profiles affords additionaladvantageous possibilities, as compared with the system of FIGS. 1 and2.

[0041] In the combination of maximum operation, P1, of the first inletvalve P with minimum operation S2 of the second inlet valve S,designated in brief as “P1+S2”, the full torque of the internalcombustion engine is available in the lower half of the rotational speedrange, whereas, at higher rotational speeds, considerable losses oftorque and power occur. However, in terms of fuel consumption, theasymmetric minimum/maximum operation of the inlet valves is alsoadvantageous, since an asymmetric flow of the inlet air with turbulenceis thereby generated, this being conducive to rapid and completecombustion. This, in turn, makes the engine tolerant to dilution withfresh air (lean combustion) or residual gases (exhaust gas circulation,variable camshaft control), which improve fuel efficiency.

[0042] In the lower rpm range, the P1+S2 combination satisfies, torque,acceleration response and allows for sufficient oil pressure for thevalve control device. At the same time, advantages arise in regards tocombustion stability and fuel consumption over double maximum operationP1+S1. The operating mode P1+S2 is suitable as a basic state or astandard setting not employing engine oil pressure. The basic state,P1+S2, is the “default state,” since this state is assumed in theabsence of engine oil pressure (for whatever reasons), and sufficientdriveability of the motor vehicle, while providing good fuel efficiency.

[0043] Investigations with motor vehicles show that four-cylindergasoline engines with manual shift transmissions are operatedpredominantly between 1500 and 3000 rpm. Speeds between idling(approximately 700 rpm.) and 1500 rpm are not used often. Under normaloperating conditions, that is to say with no excessively high oiltemperature, oil pressure is much higher at 1500 rpm than during idlingand is, therefore, sufficient to change over the actuators of the valvecontrol device. According to FIG. 4, therefore, preferably the firstinlet valve P is changed from maximum operation, P1, to minimumoperation, P3, when the engine speed reaches approximately 1500 andapproximately 3000 rpm and engine torque is light to medium. The zone ofthis operating mode, designated by “P3+S2,” is reached from the basicstate, P1+S2, by changing one of the inlet valves, P.

[0044] At high engine speed, the second inlet valve S, too, is adjustedto maximum operation, S1, to provide a maximum of fresh air. At apredetermined medium engine rotational speed, therefore, the valvecontrol device changes the second inlet valve S into. maximum operationS1, that is, the operating mode changes from P1+S2 to P1+S1. In thehydraulic valve control device described, this change takes place bypressure upon the inlet camshaft to the second inlet valve S.

[0045] According to FIG. 4, a distinction is thus made between threeoperating modes: the basic state or default operating condition, P1+S2(achievable without engine oil pressure), the low torque operating stateP3+S2 (requires engine oil pressure for the first inlet valve P), andthe high torque operating mode P1+S1 (requires engine oil pressure forthe second inlet valve S). It is advantageous that, in each operatingmode, the use of engine oil pressure is necessary at most for one of theinlet valves.

[0046] Furthermore it is particularly advantageous that the transitionsamong operating modes is executed by only one of the inlet valveschanging. In general, the transitions between the various operatingmodes, P3+S2 Û P1+S2 Û P1+S1 require not only a valve change, but alsoadjustment in the throttle valve position and spark timing to ensure aconstant torque of the engine through the change. In the methoddescribed, such a transition control is made easier in that only thechangeover is of a single inlet valve.

[0047] In summary, a preferred embodiment of the invention thus relatesto a method for operating a four-stroke internal combustion enginehaving two inlet valves, P, S, per cylinder and a corresponding primaryinlet duct 11 and secondary inlet duct 12, each inlet valve P, S beingoperated by an independent changeover device which provides either ahigher and longer valve profile or lower and shorter valve profile, thelower/shorter profile lying completely within the higher/longer valveprofile. The changeover among valve profiles is achieved using an engineoil pressure above a threshold value, by means of two independent oilcontrol valves for the first and second inlet valves P, S of a cylinderbank. In a basic state, which doesn't relay on oil pressure, the firstinlet valve, P, of each cylinder is operated with a maximum valvestroke, P1, and the second inlet valve, S, with a minimum valve stroke,S2, and with a shorter valve opening duration than the intake strokeduration. In the case of insufficient engine oil pressure for achangeover, it becomes possible, at low engine speeds, to have fulltorque by the provision of a full valve opening duration of the firstinlet valve, while at the same time the combustion properties areimproved by the generation of swirl as a result of the reduced openingof the second inlet valve.

[0048] The maximum valve stroke in minimum operation, S2, of the secondinlet valve, S, is preferably smaller than the maximum valve stroke ofthe first inlet valve, P, in maximum operation, P1, of the latter, sothat the predominant fraction of the fresh air supply takes place viathe first inlet valve, P.

[0049] Under typical operating conditions with heated-up engine oil, atmoderate engine speed and torque, the valve control device for the firstinlet valve, P, is acted upon by pressure, so that these are changedover to minimum operation, P3, with a short valve stroke and a shortvalve opening duration, which are both smaller than the correspondingsizes in the case of the second inlet valve, S, in minimum operation,S2, of the latter. The second inlet valve, S, remains without actionupon it by pressure and therefore in minimum operation, S2. The shortvalve opening durations of the two inlet valves, P, S, reduce thepumping losses in low-torque operation, and the asymmetric valveopenings ensure swirls and turbulence in the cylinder to assistcombustion.

[0050] The maximum valve stroke of the first inlet valve, P, in minimumoperation, P3, preferably amounts to one third of the maximum valvestroke of the second inlet valve, S, in minimum operation, S2, of thelatter, so that, owing to the very much higher flow resistance of thefirst inlet valve, P, the predominant fraction of the inlet air flowsthrough the second inlet valve. Furthermore, under typical operatingconditions of medium engine speed and medium engine torque, but anincreased engine oil temperature and therefore a reduced engine oilpressure which is not sufficient for changing over the valve controldevice, the control device of the two inlet valves, P, S, operate in thebasic state P1+S2. This makes it possible to have full engine torque andat the same time is conducive to obtaining the oil pressure in the restof the engine.

[0051] During idling or at a low engine speed, the engine oil pressureis typically not sufficient for changing over the valve control device,so that it likewise remains in the basic state P1+S2, ensuring theavailability of a full engine torque.

[0052] At medium to high engine rotational speeds, engine oil pressureis sufficient for changing the valve control device, so that theactuators for the second inlet valves, S, can be acted upon by pressure,so that the second inlet valves, S, can be used in maximum operation(similar to the maximum operation of the first inlet valve, P). The fulltorque and power potential of the internal combustion engine at highrotational speed is thereby available.

1. A method of operating an internal combustion engine with at least onecylinder, the cylinder having a primary intake valve and a secondaryintake valve disposed therein, the method comprising: operating theprimary valve at a first lift profile and the secondary valve at thesecond lift profile as a default condition wherein the primary valve iscapable of being switched between said first lift profile and a thirdlift profile and the secondary valve is capable of being switchedbetween said second lift profile and a fourth lift profile and theprimary and secondary valves are independently controllable.
 2. Themethod of claim 1 wherein said first lift profile has a taller valvestroke than said third lift profile and said fourth lift profile has ataller valve stroke than said second lift profile.
 3. The method ofclaim 1 wherein said first lift profile has a longer opening durationthan said third lift profile and said fourth lift profile has a longeropening duration than said second lift profile.
 4. The method of claim 1wherein a valve stroke of the secondary valve operating with said secondlift profile is less than 40% of a valve stroke of the primary valvewith said first lift profile.
 5. The method of claim 1 wherein saidthird lift profile of the primary valve and said fourth profile of thesecondary valve are caused to be selected by oil pressure acting on avalve change device.
 6. The method of claim 1 wherein the primary valveoperates with said first lift profile and the secondary valve operateswith said second lift profile when oil pressure is below an actuationpressure.
 7. The method of claim 1, further comprising: operating theprimary valve at said first lift profile and the secondary valve at saidfourth lift profile in response to at least one of engine speed andtorque.
 8. The method of claim 1, further comprising: operating theprimary valve at said first lift profile and the secondary valve at saidfourth lift profile when engine speed and torque are in a higher range.9. The method of claim 1, further comprising: operating the primaryvalve at said second lift profile and the secondary valve at said thirdlift profile in response to at least one of engine speed and torque. 10.The method of claim 1, further comprising: operating the primary valveat said second lift profile and the secondary valve at said third liftprofile when engine speed and torque are in a lower range.
 11. Aninternal combustion engine, comprising: at least one engine cylinder; aprimary inlet valve disposed in each of said cylinders; a secondaryinlet valve disposed in each of said cylinders; a first variable valvecontrol device allowing switching of the primary inlet valve between afirst and a third lift profile; a second variable valve control deviceallowing switching of the secondary inlet valve between a second liftprofile and a fourth lift profile; and an engine control unit coupled tothe engine and to said first and second variable valve control devices,said engine control unit controlling said variable valve control devicesbased on a speed and torque of the engine.
 12. The engine of claim 11wherein said variable valve control devices are actuated by engine oilpressure.
 13. The engine of claim 11 wherein said engine control unitmanages oil pressure actuation of said variable valve control devices.14. The engine of claim 11 wherein a default operating condition is whensaid primary inlet valve is operated at said first lift profile and saidsecondary valve at said second lift profile as a default condition. 15.The engine of claim 14 wherein said first lift profile has a tallervalve stroke than said third lift profile and said fourth lift profilehas a taller valve stroke than said second lift profile.
 16. The engineof claim 14 wherein said first lift profile has a longer openingduration than said third lift profile and said fourth lift profile has alonger opening duration than said second lift profile.
 17. The engine ofclaim 14 wherein said default operating condition is requested by saidengine control unit when engine speed and torque is in a medium range.18. The engine of claim 14 wherein said engine control unit causesswitching of said first valve control device to said third lift profileat a lower range of engine speed and torque.
 19. The engine of claim 14wherein said engine control unit causes switching of said second valvecontrol device to said fourth lift profile at a higher range of enginespeed and torque.